1. Field of the Invention
The present invention relates to a thermal recording head used for a facsimile or a printer. More particularly, it relates to a structure of the thermal recording head assembly.
2. Description of Prior Art
Various conventional thermal recording heads will be illustrated. A thermal recording head comprises heating elements as recording elements; lead wires and wiring which are electrically connected to the heating elements; a diode matrix required for sequentially driving the heating elements; selective terminals required for selecting groups of the heating elements; an input terminal for the input of a recording signal; and a supporting substrate for supporting the heating elements as minimum components.
FIG. 1 is a partially broken schematic view of one example of a conventional alternate lead output type thermal recording head.
In FIG. 1, the reference numeral (11) designates a heating array in which 1280 heating elements (1) are linearly arranged in a density of 6 elements per mm for a length of about 200 mm; (2) designates a lead-out wire which feeds a signal power required for the recording of the heating elements; (3) designates a supporting substrate of a ceramic plate on which the heating elements (1) and the lead-out wire (2) are fixed by sintering; (4) designates a flexible substrate; (41) designates wiring which is placed on the lower surface of the substrate and a third land part (103) to which one terminal of the diode (5) is soldered. In particular, the supporting substrate (3) and the flexible substrate (4) are press-contacted by a fitting which is not shown. The reference (6) designates a printed wiring substrate; (61) designates wiring; (104) designates a fourth land part to which the other-terminal of the diode (5) is soldered. A hole (9) for inserting the terminal of the diode (5) is formed in each of the third and fourth land parts. The wiring pattern on the flexible substrate (4) is a parallel wiring which connects the lead-out wire (2) on the supporting substrate (3) to one terminal of the diode (5). On the other hand, the wiring pattern (61) of the printed wiring substrate (6) has a matrix having m rows and n columns which connects the other terminal of the diodes (5) to selective terminals (7) or signal terminals (8). (In this example, the number of selective terminals n=40; the number of signal terminals m=32).
The selective signal of the heating elements is applied to the selective terminals (7) and the driving signal for the heating elements is applied to the signal terminals (8). In FIG. 1, 320, 60, 120, 130 and 10 are lengths having units of mm.
FIG. 2 is a circuit diagram of the thermal recording head shown in FIG. 1.
FIG. 3 is a circuit diagram of connections of three heating elements on the substrates in the circuit of FIG. 2.
In FIGS. 1 and 2, only parts of the wiring pattern, the diode and the terminals are shown. The sizes of the parts are relatively large as shown in FIG. 1.
FIG. 4 is a schematic view of a other conventional recording head. All components are formed on one surface of the supporting substrate (3) made of ceramic by a thin film technology.
In FIG. 4, 130 and 200 are lengths having units of mm. The heating element array (11) is about 190 mm long and is linearly arranged by dividing it into two groups by a center line. Each group has 4 elements per mm and has 24 selective terminals (7) and 32 signal terminals (8). The lead-out wires (2) from the heating elements (1) are respectively connected to the selective terminals (7) from 32 heating elements and the other sides of the lead-out wires (2) are respectively connected through the third joints (103) to the terminals of the diodes (5) arranged in the array. The other terminals of the diodes (5) are respectively connected through a thin film matrix circuit (42) to the signal terminals (8) by multi-layer wirings.
In FIG. 4 only part of the wiring pattern, the diode matrix, the terminals are shown. The sizes of the parts are as shown in FIG. 4.
The examples of conventional thermal recording heads shown in FIGS. 1 to 4 are typical ones used for commercial facsimile receivers. In view of market needs for facsimile devices and the development of technology related to facsimile, these factors are required: a decrease in cost, good performance and a compact size. These requirements are highly dependent upon the assembly and connections of the parts of the thermal recording head. In view of these requirements, the conventional examples shown in FIGS. 1 and 4 have the following disadvantages.
In the example shown in FIG. 1, the accuracy of the pattern of the wiring (41) on the flexible substrate (4) cannot be increased in the manufacturing process. In practice, only 3 wires per mm in the alternate lead-out wires are provided, at most. Therefore, the pitch of the heating elements (1) cannot be as dense as 8 elements per mm which is required for a highspeed facsimile receiver. A more compact size of the diode matrix connected from the flexible substrate (4) in parallel wiring can not be attained. This prevents a compact size of the facsimile body.
In the example shown in FIG. 4, whole parts are made by thin film circuit technology. Therefore, it is expensive to manufacture them at costs in mass production and it requires long processing times. In the multi-layer wirings for forming the diode matrix in the thin film circuit, the density of the lead-out wires (2) and the connecting parts are increased according to the increase of the density of the heating elements in their arrangement. Therefore, the percentage of devices without defects is substantially decreased.
The formation of the thin film circuits is made on one surface of the supporting substrate. Therefore, the joints are concentrated on the same surface whereby the plane area of each supporting substrate (3) is increased. Therefore, in order to form a compact facsimile apparatus of a transmitting type, a receiving type or a common type, the arrangement of the parts is severely limited. When the supporting substrate (3) is spread in the recording paper running direction near the recording surface (the surface for contacting the heating elements (1) with the heat sensitive paper (not shown)), the degree of spacial freedom in the design of the recording paper feeding system is disadvantageously decreased.